all pentodes...

[DummyLoad]

an all pentode amp.

about 25W P-P. output stage is plagiarized from fender "PRO 5E5". fun amp. all 3 preamp tubes are biased as pentodes. cool sounding cleans. breaks up nice but won't feedback. LOUD, of course, 25W IS loud.... ;-) 

on the breadboard, it's a simple circuit and i'm not using any coax but it's still quiet as a church mouse.

it seems as though every other 6SJ7 i have is microphonic. i sorted through a pile of 8 to get 3 preamp tubes i can live with. ugh! 

this is just an experiment...i'd like to add reverb. thinking about a 7591 to drive the tank...then it'd be the "pentOverb"? ;-)   

please feel free to comment, contribute, roast, flame, etc.. i have a flame suit. in my real job i'm a network nerd and they're standard issue. :p


respectfully,

--pete

[John]

Purty cool. I had thought about using the SJ instead of a 5879, but had read that they are for sure microphonic. Seems the metal ones would be quieter (?) I like using the octals just because they've got bigger pins to solder to. 

Neat little circuit, I'll have to give it spin!

[tubeswell]

Pretty cool. So you wired it up and recorded something?

[darryl]

an all pentode amp.

Good work. It's very satisfying to take an idea, and create a working example on the bench.
At the risk of being called pedantic . . . the 6L6GB's are beam tetrodes. Perhaps they should be replaced by EL34's.

[DummyLoad]

thanks, it does produce some nice tones. i think you will be pleased.

the original plan was to use 5879s. i just haven't finished the 9pin socket adapters for my breadboard yet. i have all the parts & material, with no excuses other than i'm just sinfully lethargic.  

currently we're running russian 6p3s reflektor mfg. outputs, i'll test with a couple of RCA 6L6GB later today.

i can't play worth a damn, so no recordings of me. i have a friend that may record for me, but he's usually pretty busy and sometimes absent minded. no guarantees.

regards,

--pete

[DummyLoad]

At the risk of being called pedantic . . . the 6L6GB's are beam tetrodes. Perhaps they should be replaced by EL34's

aha! they are called "tetrode" only to circumvent phillips patents and are constructed differently, however, they still have a suppressor grid, it's just not wires like in a EL34.

i bet EL34's would sound cool. they'll work with the 6K6 OT i'm using with a bias R adjustment, i'll give them a spin later...

thanks for the suggestion! 

--pete

[tubenit]

That looks great!  Thanks for sharing it.

 

With respect, Tubenit

[printer2]

Damn it, this is going to kill my sense of discovery! Where is my incentive to go all pentode? Oh well, hurry up, we need to hear it.  Looks good.

[rzenc]

Very interesting circuit DL!

 

Best Regards

R.

[DummyLoad]

latest mods:

input Cc was bad idea - left over from 1 tube pent. PI. go conventional 68K grid-stopper 1M grid-leak. i used a 47pF shave HF.

added NFB.

attached updated schematics.

--pete

 

[DummyLoad]

added OD stage. fun amp stuff with distortion tones that are unique... roll back on the volume & play clean, roll up volume and make it howl... tweak V2 to your liking, or build a bypass for very clean & headroom.

will fix telemetry later. yes, screen of V2 is not bypassed...not an error

respectfully,

--pete

EDIT: updated telemetry.

[printer2]

added OD stage. fun amp stuff with distortion tones that are unique... roll back on the volume & play clean, roll up volume and make it howl... tweak V2 to your liking, or build a bypass for very clean & headroom.

will fix telemetry later. yes, screen of V2 is not bypassed...not an error

respectfully,

--pete

Hey, since you are over half way there...  ..

[DummyLoad]

umm. thanks for the suggestion printer2, but i think i'll pass. i'd like to keep this simple since pentodes are so fussy. oh, and no tone stack!! 

respectfully,

--pete

[Ed_Chambley]

Pete, you told me you were a hack and would push things.  I am loving this idea.  It has been said a great amp only needs 1 knob, but it looks like this one may not even need that.

What are your plans for it.  Head or combo? I am very interested in photos of this creation.  Of course it is my intention to steal some of your ideas, but that is nothing new.

I have all these old wonderful pentodes with no place to call home.

[DummyLoad]

hi ed, thanks for the kind words.

ed, actually i have  no plans to build it. as i stated in the opening message, it's just an experiment.

if you have an old chassis laying around, something like an old PA or some such. that way you're not out much, other than some time and solder.

the metal envelope octals are so unstable and unreliable that i don't think it's worth the effort of a build, however, if i were to build it, i'd definitely shock mount all the pre amp tubes and build into a head configuration.

steal away and i'm flattered.

respectfully,

--pete 

[Ed_Chambley]

hi ed, thanks for the kind words.

ed, actually i have  no plans to build it. as i stated in the opening message, it's just an experiment.

if you have an old chassis laying around, something like an old PA or some such. that way you're not out much, other than some time and solder.

the metal envelope octals are so unstable and unreliable that i don't think it's worth the effort of a build, however, if i were to build it, i'd definitely shock mount all the pre amp tubes and build into a head configuration.

steal away and i'm flattered.

respectfully,

--pete 

Now Pete, you know I do not have anything just laying around.  It all is valuable and very well organized, just ask my wife.

David Blane taught me a solution for microphonic tubes.  Levitation.

Seriously, I have a few old PA's that will fit the bill.  What does it sound like?  Is it real greasy.  I would think not since you have it filtered quite a bit, but it seems like it may be very harmonically rich.  Recently, I have been working on trying to get that old late 50's Bakersfield tone.  Early Don Rich.  For those who are not familiar, he is the guy to the left of Buck Owens.

I have one of the essentials in the form of a 59 tele.  It is said he used a tweed twin and later used a BlackFace twin, but some old video I have shows a different amp.  It is an old tweed, but I just cannot tell which one.  It is a TV front and best guess is 5C5 Pro.  Since I have never built and octal preamp and have humdingers on the brain, this may be the ticket.

You can blame John for this new venture, I am.  

[Willabe]

Now Pete, you know I do not have anything just laying around.  It all is valuable and very well organized, just ask my wife.

 

Recently, I have been working on trying to get that old late 50's Bakersfield tone.  Early Don Rich.  For those who are not familiar, he is the guy to the left of Buck Owens.

I really like that music even though I'm not big on Tele's or at all. I need to buy some of the old stuff he put out that's now on CD. Definitely missing from my collection. In the 60's my mom used to listen to WJJD in the summer time when we'd go for a drive in the car. I still remember that.


               Brad        

[DummyLoad]

I don't know if you saw the discussion on this forum about using a single pentode as a PI, but, I can see an amp with one less tube. 

Was that the thread titled "Unusual Phase Invertor"?

--pete

[DummyLoad]

Pete,

Yes

if you're referring to the p. sulzer PI i got to work with the 6SJ7...that PI  work with and to balance. that thread is what inspired me to experiment with the pentode LTPI. PRR helped send me down the path of riotousness on biasing the screens...

--pete

[printer2]

umm. thanks for the suggestion printer2, but i think i'll pass. i'd like to keep this simple since pentodes are so fussy. oh, and no tone stack!! 

respectfully,

--pete

Just kidding, I will need to do this one myself to satisfy my curiosity.

[DummyLoad]

tone tip: trim the bass roll-off to your liking with V2 screen bypass cap. if you like jazzy clean tones, leave it off (as shown in schematic), if you like filthy, gutter & heroin laced, rock tones with even more ear splitting gain, then bypass V2 screen with a .01uF - 02uF; for fuller distortion spectrum, use a .047uF - .1uF bypass cap. if you like more mid cut, replace 100K volume pot with a an adjustable twin-t filter...

i may try 5654 pentodes. some nice feller named slucky sent me some a while back. it's incentive to finish breadboard mini 7pin socket adapters.

--pete

[Ed_Chambley]

I really like that music even though I'm not big on Tele's or at all.


               Brad        
[/quote]
This sound is the birth of the excessive mixture of major and minor and the breakaway of the guitar being a chord instrument in country music.  When they began there were not even string for electric guitar, so Don used light acoustic with a wound 3rd.  He also tuned a step down.  Of course, they could not use a strat since there was no such thing.  The guy was an insanely great lead player and would sing while doing so, but the early tone was really great.  Very raw with quite a bit of floor noise along with humming pups.  Loads of breakup and not loosing the woody transparent notes.  Still very articulate, but much nastier sounding than most people think.

My brain thinks clean clean, but listening closely this is not the case.

Looking at this experiment of Pete's, it sort of rang a bell and got me remembering the original Bakersfield tone, not the style of playing. This tone is not what most think of with tele's, but is IMO how a tele should sound.

[DummyLoad]

fooling around with screen-grid bypass cap switching to adjust LF pole of pentodes + i made a minor tweak on the PS as i wanted a bit more B+ to 6L6GB screens and the LTPI. please note updated node voltages and voltage chart.

this is probably the last iteration of this experiment. i'm probably going to build it into an old mcgohan PA chassis that that's been kicked out the way around my lab far too many times + it's already punched for 6 octal tubes.

with the switching transient suppression resistor value shown in the schematic, you need to wait a few seconds or so after the tubes start conducting before actuating the selector switch. seems like the RC chain needs some time [about 5-6 secs. more] to charge up.

position 1 has no screen-grid bypass cap, and has reduction in gain in contrast to a bypassed screen-grid so i'd consider this mainly for clean full spectrum playing as i originally intended; when in position 1 (screens un-bypassed) the LF pole is set by combination of the coupling cap and load resistor and bypass cap; switch in positions 2,3,4 the LF pole is most influenced by screen-grid bypass cap value and again, and has a significant increase in gain at and above the LF pole.

--pete

[tubeswell]

Cool pete. Thanks for sharing. That's another one for my to-do list

[DummyLoad]

Cool pete. Thanks for sharing. That's another one for my to-do list

YW, it's a fun little amp - enjoy!

kind of weird building with a screen circuit on every valve...

--pete

[DummyLoad]

an all pentode amp.

Good work. It's very satisfying to take an idea, and create a working example on the bench.
At the risk of being called pedantic . . . the 6L6GB's are beam tetrodes. Perhaps they should be replaced by EL34's.

EL34's work without any modifications. sounds raunchier, but in a good way...

schematic with updated telemetry attached.

enjoy!

--pete

[PRR]

> the 6L6GB's are beam tetrodes.

Patent on Power Pentode expired a while ago.

6L6 _is_ a pentode; just made different-enough from other pentodes and the Power Pentode Patent to fool a patent examiner, as long as RCA didn't use the word "pentode".

Once the Patent was dead, RCA could say "pentode". (Not clear where he got that passage though; IIRC RCA clung to "tetrode".)

No matter now since Pentode Pete has stuffed it with EL34.

[DummyLoad]

Not clear where he got that passage though.

tung-sol 6L6WGB datasheet. 

http://tubedata.milbert.com/sheets/087/6/6L6WGB.pdf

Pentode Pete

 

--pete

[DummyLoad]

i made a minor mod to the PS. EL34s sound better + have more headroom with a 1K shared g2 resistor and when Vg2 ~ Va. i moved the EL34 screens to the plate tap via added 1K 5W common g2 resistor. this unloaded the PS chain split after the 2K and B+ values are back up to previous 6L6GB values, a bit higher actually. EL34 g2 suck more juice than 6L6GB g2. i knew that...  

attached revised schema. voltages indicated are from memory and the voltage chart is no longer valid. i'll update later this evening.

working on electronic switching to replace the screen bypass resistors manual switch and adding a reverb ckt.

happy hacking...

--pentode-pete

[DummyLoad]

Would wiring the pentodes in triode mode count as an all pentode valve amp? 

errr... no?  :p

--pete

[darryl]

Would wiring the pentodes in triode mode count as an all pentode valve amp? 

errr... no?  :p

--pete

Looks like Pentode Pete is going to enforce high standards in his new domain. 

[Willabe]

Looks like Pentode Pete is going to enforce high standards in his new domain. 

 

[DummyLoad]

Would wiring the pentodes in triode mode count as an all pentode valve amp? 

errr... no?  :p

--pete

Looks like Pentode Pete is going to enforce high standards in his new domain. 

i have very low standards. i work in education... ;-)

--pete

[DummyLoad]

likely the last change(s) before building. RicharD wants remote switching. added that. updated telemetry with EL34's and probably going to stick with them. i tested the relay switching ckts. on a breadboard - works fab. step up/down though 5 relay selections with S2. S1 disables screen bypass altogether for clean & more headroom. planning to connect foot-switch to the amp with DIN 5 male wire/female chassis connector pair.

could have used a PIC controller, but i loathe programming and PIC's need a a clock that runs in the RF spectrum. don't like the idea of an RF source in proximity of high gain pentode preamp.

schematic(s) attached. .sch file is 2 pages, therefore there are 2 pdf files attached; one for each sheet.

thanks for following.   

--pete

[kagliostro]

Hi Pete

As always I like very much your amp ideas 

But the presence of the switch unit confuses me a lot

Please can you explain a bit more about the function of the relays and how they acts ?

Thanks

Franco

[DummyLoad]

each relay switches in a screen bypass capacitor for V2. switching S1 OFF and you have no screen bypass capacitor. for clean playing with V2 having less gain because there is no screen bypass cap. the different values of the screen bypass caps control the low-frequency cut-off points so it's like have a bass pot that has only 5 positions - the variance is from some bass to a lot of bass.

ftp://apollo.ssl.berkeley.edu/pub/cinema/04.%20Science/TTL%20Cookbook_0672210355.pdf

IC - U1 is a 74HC192 Binary Coded Decimal (BCD) up/down counter.
IOW;
BCD 0000 = decimal 0
BCD 0001 =    "       1
"     0010 =    "       2
"     0011 =    "       3
..
..
"     1000 =    "       8
"     1001 =    "       9
count up from 9 and counter wraps  to 0. conversely, count down from from 0 then counter wraps back 9.
each pulse to pin 4 counts down by 1; and each pulse to pin 5 counts up by 1.

IC - U2 is a 7445 a BCD to 1 of 10 decoder and driver .

if you apply BCD 0000 (decimal 0) to the inputs A0 thru A3 then /Y0 output is active.
if you apply BCD 1001 (decimal 9) to the   "       "    "     "  then /Y9 output is active.
each output is a PATH to ground; therefore this device is said to "sink" current. when an output is active, the relay has a path to ground and turns the coil "on". in simpler terms: if /Y0 is active then pin 1 is connected to pin 8, correspondingly then if /Y1 is active then pin 2 is connected to pin 8, etc..
only ONE of the /Y0-9 outputs is active at any time.

at initial power on the counter IC (74HC192) is at count "9" regardless of S1 position.

assume S1 is ON though. counter counts "0-9" decimal in binary since it's a BCD up/down counter.

pushing S2a we count down,

pushing S2b we count up.

as already stated, the 7445 takes the BCD and turns ON one line /Y0-9 for each corresponding count. IOW, when 0000 is input from the counter to the 7445 then /Y0 goes active and tuns on relay 5. since we have 10 count positions they are paired, remember we only have 5 relays. so outputs are strapped together; 0,5 & 1,6 & 2,7 etc..

respectfully,

--pete
    

{edit-- fixed FTP link --PRR}

[kagliostro]

MANY THANKS Pete  

Now I can understand the purpose and the way that the circuit acts

GRAZIE

Franco

p.s.: The link to the .pdf file didn't works for me

[DummyLoad]

p.s.: The link to the .pdf file didn't works for me

franco, try this one...*click me*

[kagliostro]

Thanks, now it works fine

Franco

[PRR]

> link to the .pdf file didn't works for me

Pete and all: FTP links don't work the same (in this forum software) as the common HTTP links.

The message compose box has a special button for FTP links. Looks like this:

OR: stick your FTP URL between FTP tags:

Code: [Select]

[ftp]ftp://blah.blah[/ftp]

[DummyLoad]

ok, so not so good with the digital stuff. my breadboard setup actually uses a R/S made up with 2in-NAND gate pairs with for contact conditioners that act as "pulsers". so short of the long is; my debounce ckts (R/C net) is shite.

yup, i had to add yet another chip...i tested the schmitt trigger (74HC14) de-bounce ckt. presented and attached, and it works well. at least with a piece of wire for switch, it occasionally glitches and double counts. with real momentary switches it should be much more stable. sorry for any confusion i may have conveyed.

respectfully, 

--pete

[PRR]

That type switch de-bouncer will glitch a lot.

Adding resistance before C2 C3 *may* help, or may be worse.

Depends a lot on the switch. Some willl open-close-open-close for extended time after "contact" or "break".

Lancaster's CMOS book has better debouncers, though the best want a DT switch. (But since you have Gnd and +5V in the cable, that's do-able.)

[DummyLoad]

That type switch de-bouncer will glitch a lot.

Adding resistance before C2 C3 *may* help, or may be worse.

Depends a lot on the switch. Some willl open-close-open-close for extended time after "contact" or "break".

Lancaster's CMOS book has better debouncers, though the best want a DT switch. (But since you have Gnd and +5V in the cable, that's do-able.)

schmitt works just fine. tested it with a GC switch the local fry's had in stock this evening; hasn't glitched so far and it should be OK in this application. since i want a SINGLE front panel switch and foot-switches in parallel the S/R flip-flop complicates that.

the best one and one i'm most familiar with is a S/R with 7400 or 4011 2-input NAND gates. also used in the 2 "pulser" ckts. in my proto-board.

the one i have is one like this.

also, the LED's for the 5 channel selects don't work as shown in the schematic. i used use the unused side of the relay - it was changed and i missed updating the schematic i posted. my apologies.

--pete

[DummyLoad]

ok, so the switching is done. PCB is laid out, and now we finish the chassis wiring drawings and and machining templates.

use doug's relay supply PCB - it'll work just fine. if you want a copy of the express PCB file just drop me a line, since we can't post that file type. if i get enough requests i'll pack up a zip file of everything and create a share on dropbox. share the layout for personal use if you wish under GPL. in other words, if you make any money re-marketing my crappy designs and PCB artwork; i want a cut. ;-)

in the meantime, i attached final prints of what's done and to be built; i'll post the wiring and mech drawings when done. at this time, it's to be built in a 8x24 head chassis.

respectfully,

--pete

[DummyLoad]

what's in the mill... attached drawing of wiring in pdf format. message me if you'd like to have the complete visio file. drawing is a work in progress - the jacks need to be cleaned up, etc..

for the relay board; from express PCB, prototype build option, they quoted just over $100.00 for 2, or $125.00 for 4 - neither quote included a silk screen and solder masks.

--pete